Along with recent advances in medical technology, technology for cancer therapy has also been improved extensively, and it can occasionally be seen that there are some types of cancers which show declining trend of mortality rates. However, findings of cancer development in early stage influence on the therapeutic effects, and establishment of a method which enables to detect the tumor at early stage has been desired.
As to the diagnosis of cancer, in addition to the methods which detect cancer tissues visually by ultrasound or X-ray, the method for detecting abnormality such as cell morphology in the tissue collected from a patient by immunohistological procedures, as well as biochemical, immunochemical detection methods for the dynamic state of so called tumor marker such as specific protein or gene which may cause alteration in their expression in association with the development of a specific cancer, have been known.
In these methods, the method in which the tissue is observed for its morphology by an immunohistological procedure needs for preparing tissue specimen, and takes time to ascertain the presence of cancer development, and moreover, the method will require much skill to identify the presence of cancer development from the morphology observed.
Therefore, application of the method which employs the tumor markers which can judge the presence or absence of cancer development relatively simply and objectively, has been often performed. However, since many of the tumor markers employed in the human cancer diagnosis are also expressed to some extent in the normal tissue cell, and variation of expression of the aforementioned tumor marker has to be employed as an index of malignant alteration in many cases, there always remains possibility of a wrong diagnosis.
Therefore, for the purpose of detecting presence of cancer development objectively and more correctly, it is desirable to use a substance as a tumor marker which is not detectable in non-cancer cell, but is produced only by cancerous cell. Taking a pancreatic cancer as an example, because there is no effective screening test method for pancreatic cancer at the present time, it may be too late for treatment at the time when the symptom of cancer has appeared in many cases, it would be necessary to use a specific tumor marker for pancreatic cancer to detect the pancreatic cancer in early stage.
By the way, organic anion transporting polypeptide 1B3 (OATP1B3, genetic name: SLCO1B3) is a transporter expressed on the cell membrane showing broad substrate recognition property, and is involved in uptake of various compounds comprising anti-cancer drugs into a cell. The OATP 1B3 is normally expressed specifically in hepatic cells; however, the expression will also be found in other organs in association with the tissue becoming cancerous. Up to now, it has been reported that the expression and the function of OATP1B3 affect patient's survival rate in breast cancer and prostate cancer (see, Non-patent Literatures 1 and 2). In addition, in the analysis using colorectal cancer cells, it has been reported that the expression of OATP1B3 gives the cell having resistance against apoptosis (see, Non-patent Literature 3).
From the things described above, it is conceivable that the OATP1B3 may be involved in a certain role in the cancer cell. For this reason, detection of the OATP1B3 is useful for prognostic diagnosis and efficacy evaluation of anti-cancer drug in cancer therapy, and expected to be a useful tumor marker. For example, Patent Literature 1 discloses a technology to measure expression of LST-2 in cancer tissue from female colorectal cancer patients using anti-LST-2 monoclonal antibody which recognizes C-terminal intracellular domain of LST-2 (another name of OATP1B3), and predict prognosis of the patient based on the measurement value.
However, there are many points remaining still unknown with respect to expression and function of OATP1B3 in cancer cells, and it is present situation that a method of using of OATP1B3 as a tumor marker is not well-established.